1. Field of the Invention
The present invention relates to an actuator and specifically relates to a polymer actuator which has a spiral structure and which expands and contracts.
2. Description of the Related Art
In various industrial fields, such as medical treatment, welfare, robot, and electronics, a soft actuator that is small and light weight, has good affinity with humans, and has flexible motion characteristics as in living creatures has been demanded.
As such a technique, the polymer actuator is one of promising choices. Known as the polymer actuator are a gel actuator, an ion exchange resin film-metal composite (IPMC) actuator, a composite actuator of polymer and CNT (carbon nanotube), and the like and the polymer actuator expands and contracts by converting electrical energy to mechanical energy.
Japanese Patent Laid-Open No. 2002-303303 discloses an expansion and contraction actuator having a structure in which an endless tubular tube is spirally wound. The actuator expands and contracts as a whole along the direction of the screw axis by changing the pressure of fluid introduced into the tube to thereby change the diameter of the tube. The application to medical use is assumed for flexible movement properties.
However, the actuator utilizing the pressure of a fluid as described in Japanese Patent Laid-Open No. 2002-303303 has a structure in which a rubber tubular material is used and portions other than both ends are sealed. More specifically, as long as a fluid is used, a strong structure for preventing the leak of the fluid becomes indispensable. Moreover, the introduction of the fluid into the tube requires peripheral devices, such as a compressor or a valve, which increases the size and weight, resulting in poor portability.
The tube diameter changes along the direction in which the fluid flows, and therefore the movement becomes nonuniform in the upper stream and the lower stream of the fluid. Furthermore, in terms of the structure, a higher load is likely to be applied to high pressure-loss portions in the tube, so that portions where a load is likely to be locally applied generate in driving, which has caused a problem with durability.